Crystal contact devices



July 31, 1956 E. G. JAMES Filed May 2, 1952 CRYSTAL CONTACT DEVICES |NVEN TOR q TTO'RNEY 2,757,322 Patented July 31, 1956 United States PatentOtfice CRYSTAL CONTACT Devices Emrys Gwynne James, .Pinner, England assignor to The General Electric Company Limited, Ldndon, England This invention relates to crystal contact devices. Theinvention is concerned in particular with crystal contact devices of the kind comprising an element of 'semi-conducting crystalline material arranged to co-operate with at least three metallic contact members.

It is to be understood that the term contact member in this specification does not include any metallic contact which may have a relatively large surface in contact with the crystalline element, such as the contact adapted to provide a conductive connection to the element from outside the container of the device, but only refers to contact members of the kind which are in substantially point contact with the element.

Crystal contact devices of the kind specified have previously been made experimentally, but so far as is known have not hitherto been made on a commercial scale.

It is an object of the present invention to provide a form of construction for a crystal contact device of the kind specified which will lend itself readily to manufacture on a commercial scale.

According to the invention, in a crystal contact device of the kind specified at least part of the semi-conducting element has the form of a tapered body of revolution, and each of the contact members is in the form of a wire having an end surface formed so as to have a sharp edge, the sharp edges of all the contact members being in substantially point contact with the tapered part of the element at points which lie approximately in a plane perpendicular to the axis of revolution of the tapered part of the element. 3

Preferably said end surfaces of the wires are perpendicular to the longitudinal axes of the end portions of the wires adjacent to said end surfaces, and are disposed perpendicular to the axis of revolution of the tapered part of the element.

One arrangement in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 illustrates a stage in the manufacture of crystal contact devices comprising an element of semi-conducting crystalline material arranged to co-operate with three metallic contact members; and

Figure 2 is a sectional view of one of the completed devices.

The contact members of the devices are in the form of Wires having a diameter of .075 mm., and sets of three contact members are prepared for the devices in the following manner. Referring to Figure 1 of the drawings, three long wires 1 of the required diameter are mounted so as to pass through circular holes of diameter .225 mm. in two support members 2 and 3, mandrels 4 and 5 of diameter .075 mm. being mounted in the centre of each hole so that the three wires 1 are pressed against the periphery of the holes. The three wires 1 are held so that they are angularly spaced 120 apart and are stretched so that they extend straight and parallel to each other between the two holes. Circular cylindrical beads 6 of insulating material having longitudinal axes parallel to those of the wires 1 are then moulded around the three wires 1 at points along the length between the two holes, and the wires 1 are then cut into sections each of which is mounted in one bead 6. Each bead 6 with three wires I mounted in it forms the contact member assembly of one of the devices. The three wires 1 of an assembly are ground on one side of the bead 6 so as to form on them end surfaces perpendicular to the longitudinal axes of the end portions of the wires 1, the end surfaces of all the wires 1 lying in the same plane close to one end of the bead 6.

Referring now to Figure 2, the bead 6 is in a recess '7 in one end of a support member 8 of insulating material which is in the form of a circular cylinder having an axial hole 9 of circular cross section and having embedded in it a metal tube 10. The bead 6 is disposed so that the ground ends of the three wires 1 project into the axial hole 9, the longitudinal axes of the end portions of the wires 1 being disposed substantially equidistant from the longitudinal axis of the axial hole 9, and the bead 6 is secured in this position by moulding around it a suitable synthetic resin 11.

In the axial hole 9 is mounted the semi-conducting element of the device, which is in the form of a right circular cone of germanium 12 mounted on one end of a metal cylinder 13 having a diameter slightly less than that of the axial hole 9. The element 12 is resiliently pressed against the three wires 1 by means of a spiral spring 14 which is disposed in the axial hole 9 between the metal cylinder 13 and another cylindrical metal member 15 which is soldered into the tube 10.

It will be seen that the sharp edges of the end surfaces of the three wires 1 are in substantially point contact with the conical element 12 at points which are spaced apart around one circular section of the element 12 which lies in a plane perpendicular to the axis of the element 12, this circular section having a diameter of .075 mm.

Connection is made to the element 12 by means of a wire 16 formed integral with the cylinder 13 and passing through a hole in the member 15 to which it is soldered, and connection is made to the three contact members by means of the parts of the wires 1 which lie on the opposite side of the bead 6 to the ground ends of the wires 1.

In an alternative arrangement to that described above the semi-conducting element may be mounted rigidly, the contact wires being mounted so that they bear resiliently on the surface of the element. This form of construction will generally be more convenient for crystal contact devices having more than three contact members, since it may be diflicult to ensure that the element is in contact with all the contact members in such devices if the wires are rigid and the element is mounted resiliently.

I claim:

1. A crystal contact device comprising an element of semi-conducting crystalline material at least part of which has the form of a tapered body of revolution, at least three metallic contact members each in the form of a wire having an end surface formed so as to have a sharp edge, and a support for the element and the contact members, the support holding the contact members with the portions of the contact members in the vicinity of said sharp edges laterally unconstrained and with the sharp edges of all the contact members in substantially point contact with the tapered part of the element at points which lie approximately in a plane perpendicular to the axis of revolution of the tapered part of the element.

2. A crystal contact device according to claim 1, in which said end surfaces of the wires are perpendicular adjacent to said end surfaces, and are disposed perpcn dicular to the axis of revolution of the tapered part of the element. 7 I Y 3. A crystal contact device according to claim 1, cornprising a bead of insulating material moulded around and supporting the Wires, the end portions of the wires adjacent to said end surfaces projecting a short distance from the bead.

4. A crystal contact device according to claim 1, in 10 References Cited in the file of this patent UNITED STATES PATENTS James anal- Feb. 5, 1952 James et a1 May 20, 1952 Little Aug. 12, 1952 Law- Sept. 2, 1952 

